The present invention relates generally to erasable marking compositions and more particularly to solid erasable marking compositions.
Traditionally, erasable marking compositions, e.g., highlighting inks, writing inks and correction fluids, have been provided in liquid form, as organic or aqueous solutions. In many instances, the erasability of such liquid marking compositions from conventional porous marking substrates, e.g., conventional stationery-type paper, has been achieved by including in the marking composition a component which is capable of forming a film on the the porous marking substrate in such a way as to prevent the colorant present in the marking composition from penetrating the porous marking substrate. Often, the film-forming component is a polymeric material, the polymeric material and the colorant being incorporated into an emulsion and being carefully selected so that, when the composition is applied to a porous marking substrate, the emulsion breaks causing (1) the continuous phase of the emulsion to evaporate and/or to be absorbed by the porous marking substrate, (2) the polymeric film-forming material to form a film on the surface of the porous marking substrate and (3) the colorant to associate itself with the film, as opposed to being associated with the continuous phase of the emulsion absorbed by the porous marking substrate. In this manner, the colorant can readily be removed from the substrate by stripping the film from the porous marking substrate using an ordinary pencil eraser.
To promote association of the colorant with the cohesive film, many existing liquid erasable marking compositions have exploited either (a) a charge attraction between the colorant and the polymeric film-forming material; or (b) a common hydrophobicity or hydrophilicity between the colorant and the polymeric film-forming material relative to the continuous phase of the emulsion. An example of a liquid marking composition which achieves erasability by virtue of a charge attraction between its colorant and its polymeric film-forming material is disclosed in U.S. Pat. No. 4,297,260, inventors Ferree, Jr. et al., which is incorporated herein by reference. In the aforementioned patent, there is described an erasable writing medium composition suitable for use in porous tip and ballpoint pens, the composition comprising an emulsion having a discontinuous phase of a carboxylated styrene-butadiene latex copolymer, a continuous phase of water, and a basic dye. It is stated in the foregoing patent that erasability is achieved with the foregoing composition because the majority of positively charged basic dye ions form a surface layer on the negatively charged carboxylated polymer particles of the emulsion, with only a small portion of the dye ions becoming dissolved in the continuous phase.
An example of a liquid marking composition which achieves erasability by virtue of a common hydrophobocity between its colorant and its polymeric film-forming material is disclosed in Canadian Patent Application No. 2,076,318, which was published Sep. 24, 1993, and which is incorporated herein by reference. In the aforementioned published patent application, there is described an erasable writing medium composition suitable for use in porous-tipped writing instruments, ballpoint and fountain pens, and paints, the composition comprising an emulsion having a discontinuous phase of a non-carboxylated styrene-butadiene latex copolymer, a continuous phase of water, and a water-insoluble pigment.
Additional liquid erasable marking compositions of interest are described in the following patents and patent applications, all of which are incorporated herein by reference: U.S. Pat. No. 5,217,255, inventors Lin et al., which issued Jun. 8, 1993; U.S. Pat. No. 4,940,628, inventors Lin et al., which issued Jul. 10, 1990; U.S. Pat. No. 5,203,913, inventors Yamamoto et al., which issued Apr. 20, 1993; U.S. Pat. No. 4,596,846, inventors Bohne et al., which issued Jun. 24, 1986; U.S. Pat. No. 5,120,359, inventors Uzukawa et al., which issued Jun. 9, 1992; U.S. Pat. No. 4,721,739, inventors Brenneman et al., which issued Jan. 26, 1988; U.S. Pat. No. 5,082,495, inventor Iijima, which issued Jan. 21, 1992; U.S. Pat. No. 5,004,763, inventor Imagawa, which issued Apr. 2, 1991; U.S. Pat. No. 4,753,658, inventors Okuzono et al., which issued Jun. 28, 1988; U.S. Pat. No. 4,389,499, inventor Riesgraf, which issued Jun. 21, 1983; U.S. Pat. No. 4,390,646, inventor Ferguson, which issued Jun. 28, 1983; U.S. Pat. No. 4,391,927, inventor Farmer, III, which issued Jul. 5, 1983; U.S. Pat. No. 4,687,791, inventors Miyajima et al., which issued Aug. 18, 1987; U.S. Pat. No. 4,738,725, inventors Daugherty et al., which issued Apr. 19, 1988; U.S. Pat. No. 4,760,104, inventors Miyajima et al., which issued Jul. 26, 1988; Japanese Patent No. 5-214285, inventors Kouji et al., which issued Aug. 24, 1993; PCT Application No. PCT/US92/11127, inventor Loftin, which was published Jun. 24, 1993; European Patent Application 556,668, inventors Koji et al., which was published Aug. 25, 1993; PCT Application No. PCT/US93/10231, inventors Smith et al., which was published May 11, 1994; and commonly-assigned U.S. patent application Ser. No. 08/264,565, inventor Smith, filed Jun. 23, 1994.
In addition to the above-described liquid erasable marking compositions, a solid erasable marking compositions adapted for use on paper substrates and removable with an ordinary pencil eraser is described in U.S. Pat. No. 5,300,538, inventor Loftin, which issued Apr. 5, 1994 and which is incorporated herein by reference. The composition of the aforementioned patent comprises, in a preferred embodiment, a styrene-ethylene/butylene-styrene block copolymer, a blend of waxes, a fluorescent pigment, an oil, a fatty acid, e.g., stearic acid, and a softening agent, e.g., petrolatum or natural or synthetic lanolin. The composition is preferably made by first mixing the pigment into the oil, then heating the wax, or waxes, with the block copolymer, while stirring, until both are melted, forming a clear molten liquid, and, finally, adding the pigment/oil mixture to molten liquid and mixing until homogeneous. To form the marker, the homogeneous mixture is poured into a mold and allowed to solidify. The molds are preferably first treated with a release agent, e.g., potassium stearate, to facilitate removal of the solidified composition.
Additional solid erasable marking compositions are disclosed in the following patents, both of which are incorporated herein by reference: U.S. Pat. No. 4,193,906, inventor Hatanaka, which issued Mar. 18, 1980; and U.S. Pat. No. 4,212,676, inventor Ueda, which issued Jul. 15, 1980. The solid erasable marking compositions of the aforementioned two patents are not adapted for use on conventional writing paper, but rather, are adapted for use on smooth-surfaced writing panels, e.g., metal panels, glass panels and the like, and are readily erasable therefrom with a dry eraser, such as a blackboard eraser, dry fabric, paper or the like.
Other patents of possible interest, all of which are incorporated by reference, include U.S. Pat. No. 3,576,776, inventors Muszik et al., which issued Apr. 27, 1971; U.S. Pat. No. 4,755,550, inventors Shuman et al., which issued Jul. 5, 1988; U.S. Pat. No. 4,954,544, inventor Chandaria, which issued Sep. 4, 1990; and U.S. Pat. No. 4,946,301, inventor Palm, which issued Aug. 7, 1990. The foregoing patents do not relate to erasable marking compositions, but rather, relate to solid adhesive compositions.